Various techniques are known for digital printers to provide continuous tone (monochrome or color) printing. In certain printing systems, the application of a linear gradation of ink to a substrate does not result in the appearance of a linear gradation in tone. Dither patterns are used to create tone gradations for a digital printing system that always prints uniformly equal size droplets. Images must be data corrected such that, when printed on a given printing configuration and substrate, they will appear to have a linear tone scale. In the past, it has been necessary to print and measure samples of various droplets per unit area on the paper in order to determine the appropriate transformation to apply to image data. This large number of measurements required the use of a spectrophotometer attached to a automatic traversing system.
Tone nonlinearity is a strong function of the ink and substrate selection. Additionally, various printing system configurations and substrates will require different maximum ink limits. Problems such as a loss of edge definition due to ink bleed, and difficulties in drying the substrate are factors that determine the upper ink limit. As conditions on the printing system and substrate types may change regularly, it is often necessary to determine new linearizing transformations on a regular basis.
It would be desirable to be able to determine an appropriate transformation of images to be printed on a given system in order to optimize image quality.